This review of the research literature on ability grouping and tracking draws on professional and scholarly research journals and electronic databases. Five assumptions have been used to support the recurring practices of tracking and ability grouping, but none of these assumptions has withstood close examination in 70 years of research. They are: (1) student potential can be determined by past scores on achievement or IQ tests; (2) prerequisites for achievement are obvious, simple, and easily identifiable and absolutely necessary; (3) student self-esteem is served by separating the "less able" and the "smarter" students; (4) student diversity can be accommodated through differentiated curricula; and (5) teacher work is more efficient if students are grouped homogeneously. The literature clearly shows the inadequacy of tracking and ability grouping. Research has consistently shown positive effects of the practice only for the highest ability groups, who were also given enriched curriculum and stimulating instruction. Ability grouping has been associated with discriminatory practices within the schools. A firm recommendation is made that the Fayette County (Kentucky) public schools discontinue tracking and ability grouping. (Contains 261 references.) (SLD)